In surface miners with milling rollers operating with an undershot of the above-described type, the material is loosened by the milling tools from the ground over a determined cutting depth over the entire width, carried in the direction of rotation, loosened material is guided on the outside by helically arranged guide elements in the direction of the middle of the miner, and it is then thrown onto a discharge belt, which is narrower than the width of the milling roller. The smallest possible losses shall occur during the pickup of the material and the intermediate conveying of the material. The feed movement is brought about by the traveling of the miner in the direction of mining. Surface miners with milling rollers operating with an undershot offer the advantage over surface miners with milling rollers operating with an overshot that only a small amount of dust is generated and no excessively large chunks are loosened from the ground and picked up or pushed off laterally. The maximum attainable cutting depth depends on both the roller diameter and the mounting of the milling roller and its arrangement on the surface miner.
Prior-art surface miners of the above-described type are designed such that the roller-shaped mining member engages the material to be mined with up to about one third of its diameter. This limited cutting height is due to the fact that certain assembly units for the mining member, such as the mounting of the milling roller and its drives and the drive transmission elements, e.g., the chain and the sprocket wheel, are arranged on both sides next to the roller body and a collision would therefore occur with the beds (blocks to be mined) that have not yet been stripped on the side. Such engagement ratios of the roller-shaped mining members to the material to be mined have been known in a first group of surface miners as they are disclosed in the patent specifications DE 35 04 610 C2 and DE 36 42 809 C2. The milling rollers have the same diameter over their entire length. The milling rollers are mounted by means of axle bearings on both sides.
In order for the material to be able to reach the narrower discharge belt from the milling roller, the milling tools and continuous guide plates are arranged in helical lines directed from the outside to the inside, on the one hand, and, on the other hand, they are arranged in front of the discharge belt in the direction of the material transfer in order to convey the material loosened in the outer areas at right angles in the direction of the middle area defined by the discharge belt and then to correct its flight parabola in the direction of the discharge belt if necessary. This flight parabola changes with the speed of rotation of the milling roller.
A second prior-art group of surface miners driven according to this principle is disclosed in the prospectus "Easi-Miner.RTM., Model 1224, Continuous Surface Miner" of the firm of Huron, U.S.A and in the patent specifications U.S. Pat. No. 4,536,037 and U.S. Pat. No. 4,690,461. The basic body of the milling roller has the same diameter over its entire length. The milling tools and the guide plates are arranged in helical lines on the circumference of the milling roller. Due to the material being guided from the outer areas to the middle area, the amount of material increases from the outside toward the middle. However, since the milling roller has the same diameter over its entire length, the space between the jacket of the milling roller and the cutting circle diameter is utilized increasingly less to the outside. This is disadvantageous because lower stability is reached, in principle, at equal wall thickness in the case of smaller roller diameters and to obtain a sufficiently large space in the middle of the milling roller for picking up and forwarding the material being conveyed, the milling tools must be made correspondingly long to obtain a sufficiently large cutting circle diameter. The milling roller is mounted on both sides. The drive is transmitted on one side from the outside from a motor arranged above via a chain drive to the milling roller. To make it possible to reliably transfer the material from the milling roller onto the discharge belt, a chute with a broad takeup opening is provided here as well, and this chute narrows in the direction of the discharging belt and thus corrects the flight parabola of the material into the direction of the discharge belt in the case of deviations. The flight parabola of the material also changes with the speed of rotation of the milling roller.
The above-mentioned two types of miners are designed preferably for hard material, which is picked up by the miner after the milling process and is loaded on trucks traveling along. With miners of such a design for mining deposits according to the surface mining process, an increase in the mining performance is achieved after the maximum cutting height has been reached by increasing the feed speed of the miner. The drawbacks of increased chassis wear and energy consumption, which is due to the faster movement of the entire miner, are thus accepted. Furthermore, the connection of the miner to a belt system for continuous mining is possible with difficulty only at these high velocities of travel. If this type of surface miner were used to mine material in greater cutting depths, it would be necessary to provide means that prevent the loosened material from being pushed off to the side from the area of the milling roller.
Another surface miner with a milling roller designed as a roller-shaped mining member, which can operate in a cutting height that is approximately equal to half the diameter of the mining member has been known from the patent specification U.S. Pat. No. 5,092,659. Since the bearings for the milling roller are located within the basic body of the milling roller, this cutting height can still be increased somewhat even in the case of optimization of the drives arranged on the outside above on both sides of the milling drum. However, the arrangement of the drives next to the milling roller requires special measures for protection against harmful mechanical effects. The milling roller operates with an overshot. The cut material is carried to the upper area of the milling roller, from which it falls into the interior through the grid-like jacket of the roller as a consequence of its gravity. A cross belt with a chute is arranged there, from which the material is carried to the outside by a cross belt and is transferred onto a conveyor belt conveying it farther away. To have sufficient space for this, a block must already have been mined on this material discharge side. A specific mining technology must therefore always be used with such a miner.
To ensure that the loosened material will also fall reliably into the interior through the grid-like jacket of the roller, a maximum speed of rotation must not be exceeded. Furthermore, moist and clayey soils adversely affect the maximum possible output of the miner.
Furthermore, a surface miner similar to that described above has been known from the patent specification U.S. Pat. No. 5,730,501. The material having fallen through the grid structure of the basic body of the milling roller as according to the above-described prior-art solution is discharged by the cross belt from the interior of the milling roller, transferred to a vertical lifting screw, which assumes the function of an intermediate conveyor, and is passed on by this to a removing conveyor. In order to have sufficient freedom of movement for the lifting screw in the mining area during the feed movement of the miner, an additional milling roller is arranged rotatably in a vertical axis of rotation at the lower end of the lifting screw. The maximum cutting height of the main milling roller is thus limited by the cutting height of the smaller milling roller that is additionally needed.
What was said above applies to the limited output and the disadvantageous effect in the case of moist and clayey soils.
A surface miner, in which a roller-shaped mining member operating with overshot comprises four bucket wheels arranged in a common axis and being arranged in front of the miner in the direction of travel, is described under 4 in the DE journal Braunkohle, 1990, No. 3, pp. 28 to 34. These bucket wheels are fastened to the miner by two brackets, which are arranged each between the outer and middle bucket wheels. Due to the drives being accommodated in the interior of the bucket wheels and due to the feed lines for these drives being displaced into the free space together with the brackets between two adjacent bucket wheels, the necessary freedom of movement is achieved on the side of the mining member. A mining member thus designed requires more material for its manufacture and is therefore heavier than the above-described ones. However, cutting heights that are greater than the radius of the mining member can be reached with this mining member. However, the consequence of the overshot mode of operation of the mining member is that chunks that cannot be picked up by the miner can be picked up and dust is generated. Material loosened in the outer areas of the pickup member is partially pushed off to the outside and forms piles there over the entire length next to the mining section. To prevent loosened material being conveyed from penetrating via the intermediate spaces into the interior of the mining member and from adversely affecting the mining process and/or from leading to an additional wear of moving parts, special precautionary technical measures are taken to retain the material being conveyed. The brackets between the bucket wheels do not make it possible to provide a transverse conveying of the material directed toward the middle in the area of the mining member. As a result, additional cross belts are needed behind the roller.